The present invention relates to the field of dispersions of inorganic nanoparticles.
The present invention relates more particularly to stable dispersions of inorganic nanoparticles and also to their use and preparation and, furthermore, to systems comprising these dispersions. The present invention further relates to a method of stabilizing dispersions of inorganic nanoparticles.
For the purpose of improving the mechanical properties of coating and dispersion systems (as, for example, of paints, inks such as printing inks, coatings, etc.) and of plastics, more particularly for the specific purpose of enhancing their wear properties, such as scratch resistance or the like, the incorporation of additives and fillers is part of the core knowledge of the skilled person. Increasingly here dispersions of inorganic nanoparticles are being employed. Some of these nanoparticles (examples being TiO2 and/or ZnO) are also used in order to improve the UV stability.
One problem frequently associated with conventional dispersions of inorganic nanoparticles is the inadequate storage stability, and more particularly the tendency towards sedimentation. This phenomenon may ultimately result in the sedimented nanoparticles undergoing agglomeration or caking with one another after prolonged periods of storage, and forming a solid residue which can no longer be stirred up and/or broken down, with the consequence that, eventually, the dispersions can no longer be used at all. The sedimentation tendency is promoted by the high densities of the inorganic nanoparticles. Inorganic nanoparticles having particularly high densities, in the range from 5 g/cm3 to 6 g/cm3 or even more, such as inorganic particles based on zinc oxide, antimony/tin oxides (ATO), indium/tin oxides (ITO) or the like, for example, display a particularly strongly pronounced tendency to form sediment.
Consequently attempts have also been made in the prior art to make such dispersions of inorganic nanoparticles storable or sedimentation-stable through addition of specific additives, more particularly stabilizers. A critical disadvantage of the stabilizers or additives used in the prior art, however, is that their incorporation typically entails a disadvantageous adverse effect on the flow capacity properties or the Theological properties of the dispersions. Frequently, indeed, there is an unwanted solidification of the dispersions stabilized in this way. Occasionally, however, a syneresis is observed, in tandem with unwanted phase separation as a result of the sedimentation. Systems of this kind are then no longer suitable for the aforementioned applications.